In electronic circuit boards, even though the great majority of interconnections may be implemented as printed conductive traces, there are special circumstances in which it would be advantageous to interconnect particular components through insulated hookup wire. For example, the usual printed traces often prove unsatisfactory for routing a high speed digital signal from one region of the circuit board to another region due to inherent properties of printed traces which severely limit attempts to utilize them as high frequency transmission lines. The main shortcoming is susceptibility to crosstalk and r.f. interference even in attempts to form a "balanced" line from a pair of parallel traces, especially if they are unshielded at the circuit board surface in a usual microstrip configuration.
A classic solution to this type of problem is to form integral pseudo-coaxial signal paths within the circuit board by adding several additional circuit board layers to form buried stripline printed traces as signal paths sandwiched between ground plane shield layers in a multilayer circuit board configuration, imposing as a tradeoff penalty the greatly increased cost, complexity, fabrication difficulty and potential unreliability of a multilayer circuit board.
An alternative classic solution involves the addition of discrete runs of rigid or flexible coaxial cable: this is also costly and complex, usually entailing a great deal of skilled manual fabrication and assembly, and often suffers from impedance compromises along printed trace interface runs between the ends of the coaxial cables and the actual component terminals involved.
A third alternative, which has not been fully exploited heretofore, utilizes an unshielded twisted pair of insulated hookup wires serving as a balanced transmission line. The twisted pair configuration, by virtue of an inherent antenna effect cancellation property, provides superior crosstalk isolation over a single unbalanced line or parallel pair configuration such as microstrip lines formed on the surface of a circuit board, and, while not fully equivalent to shielded coaxial cable, twisted pair transmission lines, particularly in the novel implementation of this invention, will in many instances provide fully satisfactory signal transmission performance along with considerable cost, simplification, producibility and reliability benefits by avoiding the need for multilayer circuit boards and/or coaxial cables.
There are other situations where it may be preferable to fabricate a circuit board utilizing point-to-point hookup wiring throughout, for example, in realizing a preliminary "breadboard" model for evaluation and/or experimentation in advance of the availability of a "tooled-up" printed circuit version.
Point-to-point hand wiring as sometimes practiced in low volume production of circuit boards is generally tedious and costly, particularly where wire ends must be individually wrapped manually onto pins or terminal lugs and soldered individually.
As an alternative to hand wiring, a well known "wire wrap" technique involves wrapping the stripped ends of special hookup wire in a long tight spiral around special square elongated contact posts; frequently it is necessary to mount components such as DIP (dual inline packaged) devices, in special sockets having the required square posts, which, when wired correctly with a wrap of sufficient length, are supposed to provide reliable connections without soldering. "Wire wrap" is generally incompatible with standard dip or wave soldering since the presence of wiring on the side opposite the "component" side, i.e. on the "trace" side, which is normally immersed in molten solder at a temperature which would destroy the hookup wire insulation; therefore, any connections requiring soldering must be done individually, typically by hand.
"Wire wrap" is generally useful only at relatively low digital rates or frequencies, having proven unsuitable for handling some families of high speed logic such as ECL (emitter coupled logic) due to degradation of rise and fall times due to signal line termination impedance mismatches introduced by the elongated square posts.
The present invention provides a beneficial supplement, and in some instances a viable alternative, to a range of conventional circuit board practices including printed circuitry as well as hand wiring and wire wrapping.